A conventional writing instrument of this kind is disclosed as a mechanical pencil in Japanese Utility Model Publication No. 50156 of 1992 (Heisei 4), in which an engaging sleeve formed with an engaging portion is inserted between a head opening being provided at a front end portion of a lead advancing mechanism and an outer step portion provided behind the head opening. The engaging portion of the engaging sleeve for engaging the outer barrel is mounted between the head opening of the lead advancing mechanism and a front end of the outer barrel so that the lead advancing mechanism can be held by the outer barrel.
However, in such a conventional mechanical pencil, the engaging portion is exposed out of the outer barrel and so injures outward appearance, because the engaging portion is mounted between the head opening of the lead advancing mechanism and a front end of the outer barrel.
Accordingly, it is an object of the present invention to provide a writing instrument in which outer appearance thereof is not injured and assembling thereof is easy.